Business, science and entertainment applications depend upon computing systems to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
Tape drive systems for linear tape formats such as Linear Tape Open (LTO) typically have one or two heads, each head having an array of transducers for writing to and reading from the tape. For example, a state-of-the-art multichannel tape magnetic recording head today contains 16 data channels and 2 servo reader channels in each of two bidirectional modules. Current practice is to fabricate the servo reader channels using the same shield-to-shield gap dimensions as those in the data reader channels, as this minimizes fabrication costs.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head's reading and writing transducers used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM® Corporation. The MR sensor transduces magnetic field changes in an MR stripe to resistance changes, which are processed to provide digital signals. Data storage density can be increased because an MR sensor offers signal levels higher than those available from conventional inductive read heads for a given bit area. Moreover, the MR sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity.
The quantity of data stored on a magnetic tape may be increased by increasing the number of data tracks across the tape, which also decreases the distance between adjacent tracks and forces key dimensions of read/write heads to be physically smaller. More tracks are made possible by reducing feature sizes of the read and write elements, such as by using thin-film fabrication techniques and MR sensors.
Similarly, as technology advances, the data reader gaps continue to be optimized to thinner dimensions, providing for detection of higher linear densities of magnetic transitions along the tape. Meanwhile, the linear density of servo tracks on tape is typically unchanged over the various generations of a family of products, and often is more than a factor of 10 lower than the data channel linear density. Also, the trend is toward thinner magnetic coatings on tape, again optimizing data channel characteristics but compromising servo channel signal amplitudes, especially with low density signals and the trend toward decreasing reader gaps. Using the same thin gap in the servo reader channel transducers as the data readers results in both suboptimal performance for the servo channels (in the form of undesirably low signal amplitudes due to the unnecessary thinness of the gaps) and increases reliability concerns for the servo channels, e.g., increased risk of shorting between the MR sensor and metallic magnetic shield (if, for example, a scratch occurs) due to the unnecessary thinness of the gaps.
One proposed solution to the problems described above is to build multiple read channels separately rather than simultaneously. However, such heads are much more expensive to fabricate than heads where all reader channels are created simultaneously.
Another proposed solution includes writing servo-written tape using more elaborate means to increase servo amplitude, e.g., bipolar servo patterns and/or DC erased tracks. However, implementation of these new servo patterns require new servo writing hardware for tape manufacture as well as modified signal detection algorithms in the tape drives.
There is accordingly a clearly-felt need in the art for a magnetic head assembly with definable reader gaps selected to optimize performance and/or reliability. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.